1. Field of the Invention
The present invention relates to an organic electroluminescence display device in which an electric field is applied to an organic electroluminescence element provided with an organic electroluminescence layer between a pair of electrodes to cause to emit light, and particularly relates to a layered structure of an organic electroluminescence element.
2. Description of the Related Art
Liquid crystal display devices (LCD), plasma display devices (PDP), field emission displays (FED), organic electroluminescence display devices (OLED), and the like are currently either in practical use or in the research stage for practical use as flat panel display devices. Among these, organic electroluminescence display devices are display devices having considerable promise as typical future self-illuminating display devices that are thin and lightweight. There are so-called bottom emission and top emission types of organic electroluminescence display devices.
In a bottom emission organic electroluminescence display device, an organic electroluminescence element is configured having a light-emitting structure in which a transparent electrode as a first electrode or as one electrode, an organic electroluminescence layer (also called an organic multilayer film) that emits light by the application of an electric field, and a reflective metallic electrode as a second electrode or another electrode are sequentially layered on a transparent substrate for which a glass substrate is preferably used. Numerous such organic electroluminescence elements are arrayed in the shape of a matrix and sealed by an insulating substrate, also called a sealed can, and the light-emitting structure is isolated from the external atmosphere.
Carriers (electrons and positive holes) are then injected into the organic electroluminescence layer, and the organic electroluminescence layer is caused to emit light by application of an electric field between the two electrodes in which, e.g., a transparent electrode is an anode and a reflective metallic electrode is a cathode. The emitted light departs from the transparent substrate to the exterior.
By contrast, in a top-emission organic electroluminescence display device, an organic electroluminescence layer is caused to emit light by application of an electric field between two electrodes, wherein one of the electrodes described above is a reflective metallic electrode, and the other electrode is a transparent electrode. The emitted light is emitted from the other electrode (transparent electrode) described above. A transparent substrate is used as a sealed can in a top emission display device.
In relation to this type of organic electroluminescence display device, the configuration of the electron injection side in which the layer structure of the organic electroluminescence element is formed in the sequence of an anode, a hole injection layer, a hole transport layer, and a light-emitting layer is disclosed in Japanese Laid-open Patent Publication No. 2006-156997.
Specifically, an organic electroluminescence element is disclosed in which an organic electroluminescence structure having a hole injection electrode, an electron injection electrode, and an organic layer that includes one or more types of light-emitting layers disposed between the electrodes is accommodated in an airtight case; one or more types of calcium hydride, strontium hydride, barium hydride, and aluminum hydride are placed in the airtight case; and the electron injection electrode contains one or more types of either alkali metal and either alkaline-earth metal.
Additionally, although there is a description in Japanese Laid-open Patent Publication No. 2006-156997 stating that an alkali metal may be contained in the electron transport layer and the light-emitting layer, there is no description that alkali metal is contained in the hole injection layer. Furthermore, although there is a concept related to a carrier generation layer in Japanese Laid-open Patent Publication No. 2006-156997, only the layered structure between the electron transport layer and the cathode is disclosed, and no consideration whatsoever is given to the layered structure between the anode and the hole transport layer.